Fabricating integrated circuit devices involves forming multiple layers of conducting, semiconducting, dielectric, and insulting materials on a substrate. During fabrication, the substrate is typically planarized at various stages to make it level and uniform, and eliminate recesses, protrusions, scratches, and other undesirable topology, which can cause step coverage problems for the deposition of a subsequent material layer and depth of focus problems that impair photolithographic processes used to form sub-micron features.
Chemical-mechanical polishing and chemical-mechanical planarization processes, both of which are referred to herein as “CMP” processes, are abrasive techniques that typically include the use of a combination of chemical and mechanical agents to planarize, or otherwise remove material from a surface of a micro-device workpiece (e.g., wafers or other substrate) in the fabrication of micro-electronic devices and other products. A planarizing or polishing pad (“planarizing pad”) is used with a chemical solution along with abrasives, which may be present in the solution as a slurry or fixed within the pad itself, to mechanically remove material from the workpiece surface.
FIG. 1 illustrates a conventional chemical-mechanical planarization apparatus 10 with a circular table or platen 12, a carrier assembly 14, and a planarizing pad 16. An underpad or subpad 17 can be attached to the planarizing pad 16 or to a surface of the platen 12 for supporting the planarizing pad 16. A drive-assembly 18 rotates the platen 12 (indicated by arrow “A”) and/or reciprocates the platen 12 back and forth (indicated by arrow “B”), and the motion provides continuous movement of the planarizing pad 16 relative to a workpiece 20 (e.g., a wafer) secured onto a substrate holder 22. In the illustrated embodiment, an actuator assembly 24 is coupled to the substrate holder 22 to provide axial and/or rotational motion to the substrate holder 22 as indicated, respectively, by arrows “C” and “D”. Also as shown, the substrate holder 22 is coupled by an arm 28 to a sweep actuator 26 that rotates (indicated by arrow “E”) to “sweep” the substrate holder 22 along a path across the planarizing surface 30 of the planarizing pad 16. In operation, the workpiece 20 and/or the planarizing pad 16 are moved relative to one another allowing abrasive particles in the pad or slurry to mechanically remove material from the surface of the workpiece 20, and reactive chemicals of the planarizing solution 32 on the surface 30 of the planarizing pad 16 to chemically remove the material.
The apparatus 10, shown in FIG. 1, also includes a second carrier assembly 34 having a carrier 36 for a conditioning pad 38 that is brought into contact against the planarizing surface 30 of the planarizing pad 16. The conditioning pad 38 abrades the surface 30 of the planarizing pad to abrade it, which prevents glazing of the pad surface and provides a fresh surface for polishing.
In the process of chemical-mechanical polishing, the incoming substrates have certain topography as a result of the features that are fabricated on them, and the overlying films deposited over the features. In a production flow, it is desirable to maximize throughput, which for CMP processing is to remove a material layer and/or produce a planar surface on a substrate as quickly as possible. Many CMP processes require a process endpoint based upon removal of topography, degree of planarization of the workpiece surface, and/or the transition from one material layer to a next material layer, for example, from an oxide layer to a nitride layer. It is important to accurately stop CMP processing at a desired endpoint so that the workpiece substrate is not under-planarized, requiring re-polishing, or over-planarized, which can cause “dishing” or completely destroy components on the substrate. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is planar and/or enough material has been removed from the substrate to expose a desired underlayer or to form the desired components, for example, a shallow trench isolation area, a contact, etc.
There are various conventional methods for determining the endpoint of a CMP process. One method involves using an estimated polishing rate based upon the polishing rate of identical substrates planarized under the same conditions to determine the planarizing period of the particular substrate at hand. This method may not produce accurate results due to differences in polishing rates and variations from one substrate to another.
In another method for determining the endpoint of a CMP processing, the workpiece is removed from the pad and a change in thickness of the substrate is measured. However, interrupting a CMP process to remove the workpiece from the pad reduces CMP processing throughput and can cause damage to the workpiece.
There are also apparatus for monitoring planarizing during a process cycle. Some apparatus incorporate a sensor for measuring reflectance of the surface of a wafer to infer that a process point has been reached, for example, according to film thickness or the transition from an opaque to a transparent surface.
Other methods of endpointing a CMP process include the use of acoustic emission sensing in a wafer carrier. However, incorporating sensors into the carrier poses problems with signal dampening. Such a set-up is also not practical in manufacturing applications due to the need to isolate the carrier from the carrier using a urethane containing material, which leads to high signal attenuation.
Therefore, it would be desirable to develop an apparatus and method for more accurately monitoring and endpointing planarization and polishing of microelectronic substrates.